Master Neutral Buoyancy: The Importance of Horizontal Trim (Simple Vector Physics)

[Steve_C]

That's funny, a HP100 is O.8 inches shorter than an AL80

I just went out to my garage where I have a pair of AL80s and a pair of HP100s. Standing upright the HP100 is 3 inches sorter than the AL 80.

---------- Post added December 24th, 2015 at 09:04 PM ----------

Cylinder	Service Pressure (psi)	Diameter (inches)	Height* (inches)	Weight Empty (pounds)	Buoyancy Full : Empty (pounds)
F7 Steel HP80	3442	7.25	20.8	28.3	- 8.1 : - 1.7
F7 Steel HP100	3442	7.25	25.3	34.0	- 8.4 : - 0.6
F7 Steel HP120	3442	7.25	29.1	39.2	- 8.8 : + 0.7
F8 Steel HP117	3442	8.00	24.2	37.6	- 9.1 : + 0.2
F8 Steel HP133	3442	8.00	26.9	42.4	- 9.1 : + 1.5
Comparison Only - Aluminum 80	3000	7.25	26.1	31.9	- 1.8 : + 3.2

From the DGX website, the current Faber steel tanks

My HP 100 are XS Scuba and the tank, ignoring valves is 23.5.

 

[scubadada]

And older Faber 100s, PST E7 100s (3442psi) and older PST 100s (3500psi), are all right at 24".

So, I guess it depends on which HP100s you're talking about.

Shouldn't you be driving to Florida, or are you already there? Merry Christmas

---------- Post added December 25th, 2015 at 03:54 AM ----------

I just went out to my garage where I have a pair of AL80s and a pair of HP100s. Standing upright the HP100 is 3 inches sorter than the AL 80.

---------- Post added December 24th, 2015 at 09:04 PM ----------



My HP 100 are XS Scuba and the tank, ignoring valves is 23.5.

Aren't the old 100s a little more negative than the current ones also? I liked that

 

[Steve_C]

[QUOTE}
Aren't the old 100s a little more negative than the current ones also? I liked that[/QUOTE]

Don't know. The only HP100 I have ever dove. Just know that I really like them. Have dove a number of other rental tanks. Usually just tell the renters my weighting with the HP100, they make a recommendation. I use it on dive one. Often take off a little off their recommendation on subsequent dives.

Dove a tank in Greece. Short and fat. Looked like one of its parents was a propane tank. Liked the feel of that tank too.

 

[stuartv]

Shouldn't you be driving to Florida, or are you already there? Merry Christmas

LOL Merry Christmas to you!

I am on the way. Posting from a hotel room in NC.

 

[sibermike7]

I am a "rather large" (read as fat) guy, but my legs are still very athletic. This automatically makes them sink in both fresh and salt water... Given this issue, my tank is placed very high on my wing to "tilt" or "compensate" forward to help my trim in the water

Thanks BHB! You've made my day. Wait until my wife hears....

"Honey! Did you hear that?? My legs are NOT fat, they're athletic!!!"
Merry Christmas!

 

[Hatul]

OK NetDoc, I'm ready for the next installment.

 

[PhatD1ver]

I've changed the term to "propulsion". I doubt that anyone but a jet pilot was confused by this, but now everyone should be able to understand the concepts.

I'm a helicopter pilot and I knew what you were saying all along, if they have problems with this, I can't wait for the other three sections.

 

[The Chairman]

I'm a helicopter pilot and I knew what you were saying all along, if they have problems with this, I can't wait for the other three sections.

it's funny, but my dad was a helicopter pilot too. USMC medivac pilot for a MASH unit in Korea. Something about his IQ being too high to strap all those explosives and play Wile E Coyote on a rocket. I guess being able to hover must be in my blood.

 

[TheHobster]

Doc,

First, this is my first time on SB in a couple months. Great thread. Much needed and informative.

Will you be using the "teeter-totter" principle for trim? I used to say something along the lines of "your center of buoyancy (CoB) is roughly your stomach. So we say that is the fulcrum of the teeter totter. If we are heavy, we add air to our BC, which is ABOVE the CoB or fulcrum. So what does that do to everything above the CoB or fulcrum? It raises it, and lowers everything below the CoB/fulcrum. When we kick, where does the propulsion push us? Up. What happens to the air in our BC, and our wetsuit when we ascend? It expands, we become positive and we float"

followed by "If we are light, we add weight to our BC or on a weight belt. That is BELOW the CoB or fulcrum, so what does that do to everything below the CoB or fulcrum? It pushes it down. So when we kick, where is the propulsion push us? Up. What happens to the air in our BC, and our wetsuit when we ascend? It expands, we become positive and we float"

Of course, being part Italian I use my hands, pens, etc to explain this as well.

 

[The Chairman]

You'll love bubble management. It's a way to stop the teeter... or was that the totter?